update README

Author: debugly

README.md

@@ -120,7 +120,10 @@ If cloning repositories from GitHub is slow, or if you need to use an internal p
 
 | Lib Name   | Current Version | Repository URL                                           | Mirror Repository URL                                    |
 | ---------- | --------------- | -------------------------------------------------------- | -------------------------------------------------------- |
-| FFmpeg     | 7.1.1           | https://github.com/FFmpeg/FFmpeg.git                     | export GIT_FFMPEG_UPSTREAM = git@xx:yy/FFmpeg.git        |
+| ffmpeg7     | 7.1.1           | https://github.com/FFmpeg/FFmpeg.git                     | export GIT_FFMPEG_UPSTREAM = git@xx:yy/FFmpeg.git        |
+| ffmpeg6     | 6.1.1           | https://github.com/FFmpeg/FFmpeg.git                     | export GIT_FFMPEG_UPSTREAM = git@xx:yy/FFmpeg.git        |
+| ffmpeg5     | 5.1.6           | https://github.com/FFmpeg/FFmpeg.git                     | export GIT_FFMPEG_UPSTREAM = git@xx:yy/FFmpeg.git        |
+| ffmpeg4     | 4.0.5           | https://github.com/FFmpeg/FFmpeg.git                     | export GIT_FFMPEG_UPSTREAM = git@xx:yy/FFmpeg.git        |
 | ass        | 0.17.3          | https://github.com/libass/libass.git                     | export GIT_ASS_UPSTREAM = git@xx:yy/libass.git           |
 | bluray     | 1.3.4           | https://code.videolan.org/videolan/libbluray.git         | export GIT_BLURAY_UPSTREAM = git@xx:yy/libbluray.git     |
 | dav1d      | 1.5.1           | https://code.videolan.org/videolan/dav1d.git             | export GIT_DAV1D_UPSTREAM = git@xx:yy/dav1d.git          |